Place the numbers from 1 to 8 on the following board so that the number placed in each red box must be equal to the sum of the numbers placed in the white boxes that surround it:
To reach the solution we can perform the following reasoning: It is obvious that the number 8 cannot be placed in the white boxes since any sum with this value would return a number greater than 8. From this, we also arrive at the conclusion that 7 must go in a red square since placing it in a corner any sum with this value would return a number greater than or equal to eight and we know that 8 we already have it placed in a red box.
By a similar reasoning we conclude that 1 and 2 must go in the corners. From this we place these values and we deduce the rest little by little.